This disclosure is directed to pulsed electrical stimulation of nerves or nerve bundle in the sacral or pelvic region, or branches of such nerves or portion thereof, to provide therapy for erectile/sexual dysfunction, prostatitis, pain originating from prostate pathology, and chronic pelvic pain. The method and system of this invention comprises both implantable and external components. The nerve stimulation may be to different nerves in the sacral and/or pelvic regions of the body. To provide therapy for erectile dysfunction, the selective neurostimulation is to cavernous nerve or pudendal nerve or its branches or portion thereof. To provide therapy for prostatitis or chronic pelvic pain, the selective neurostimulation is provided to one or more of the pudendal nerve or its branches or portion thereof, the prostatic plexus or its branches or portions thereof, or the sacral splanchnic nerve or its branches or portions thereof.
General anatomy of the sacral region is shown in conjunction with FIG. 1. The relation of sciatic nerves 24 and pudendal nerve 20 in relation to sacral region is also shown in FIG. 1. There are five pairs of sacral nerves in the body. A more detailed anatomy of the five sacral nerves, their branches including the pudendal nerve is depicted in FIG. 2.
FIG. 3 and FIG. 4 show more details of the relevant anatomy. The male sexual organ (FIG. 4) and the innervation to the penis via cavernous nerve 28 is shown in FIG. 3 in more detail. Despite the obvious structural differences between the female and male reproductive organs, their neural regulation is surprisingly similar. Sexual arousal of adult men and women can result from erotic psychological and sensory stimuli, and from direct tactile stimulation of the external sex organs. A full sexual response cycle consists of arousal followed by plateau, orgasm, and resolution phases. Although the duration of each phase can vary widely, the physiological changes associated with each one are relatively consistent. Neural control of the sexual response comes in part from the cerebral cortex but the spinal cord coordinates this brain activity with sensory information from the genitals and generates the critical outputs that mediate the sexual responses of the genital structures.
The major external and internal sex organs are depicted in FIG. 5. Sexual arousal causes certain parts of the external genitals of both women and men to become engorged with blood, and thus to swell. In women, these structures include the labia and the clitoris; in men, it is primarily the penis. The external genitals are densely innervated by mechanoreceptors, particularly within the clitoris and the glans of the penis. Adequate stimulation of these sensory endings can, by itself be enough to cause engorgement and erection. The evidence that engorgement can be generated by a simple spinal reflex is that most men who have suffered a complete transection of the spinal cord at the thoracic or lumbar level, can nevertheless generate an erection when their penis is mechanically stimulated. The mechanosensory pathways from the genitals are components of the somatosensory system, and their anatomy follows the usual pattern: Axons from mechanoreceptors in the penis and clitoris collect in the dorsal roots of the sacral spinal cord (FIG. 5). They then send branches into the dorsal horns of the cord, and into the dorsal columns, through which they project toward the brain.
Engorgement and erection are controlled primarily be axons of the parasympathetic division of the autonomic nervous system (ANS). Within the sacral spinal cord, the parasympathetic neurons can be excited by either mechanosensory activity from the genitals (which can directly trigger reflexive erection), or by axons descending from the brain (which account for responses mediated by more cerebral stimuli). Engorgement of the clitoris and penis depend on dramatic changes in blood flow. Parasympathetic nerve endings are thought to release a potent combination of acetylcholine, vasoactive intestinal polypeptide (VIP), and nitric oxide (NO) directly into the erectile tissues. These neurotansmitters cause the relaxation of smooth muscle cells in the arteries and the spongy substance of the clitoris and penis. The usually flaccid arteries then become filled with blood, thereby distending the organs. (Sildenafil, a drug with the trade name Viagra, is a treatment for erectile dysfunction that works by enhancing the effects of NO). As the penis becomes longer and thicker, the spongy internal tissues swell against two thick elastic outer covering of connective tissue that give the erect penis its stiffness. In order to keep the organs sliding easily during copulation throughout the plateau phase, parasympathetic activity also stimulates the secretion of lubricating fluids from the woman's vaginal wall and from the man's bulbourethral gland.
Completing the sexual response cycle requires activity from the sympathetic division of the autonomic nervous system (ANS). As sensory axons, particularly from the penis or clitoris, become highly active, they together with activity descending from the brain, excite sympathetic neurons in the thoracic and lumbar segments of the spinal cord. In men, the sympathetic efferent axons then trigger the process of emission. Finally during ejaculation, a series of coordinated muscular contractions expel the semen from the urethra, and this is usually coincident with the intense sensations of orgasm. In women, stimulation adequate to trigger orgasm probably also activates the sympathetic system. Sympathetic outflow causes the outer vaginal wall to thicken and, during orgasm itself, triggers a series of strong muscular contractions. Following an orgasm, some time must pass before another orgasm can be triggered in men. The orgasmic experience of women tends to be considerably more variable in frequency and intensity. The resolution phase, which ends the sexual response cycle, includes a draining of blood from the external genitals through veins, and a loss of erection and other signs and sensations of sexual excitement.
Medical studies have shown that electrical stimulation of the cavernous nerve provides treatment for erectile dysfunction in humans. FIG. 6 depicts the location of cavernous nerve 28 at a point convenient for placing electrodes for neurostimulation. For implanting a system for erectile dysfunction, an incision is made for exposing the nerve tissue. As depicted in FIG. 7, the cavernous nerve 28 is exposed, and the distal portion of the lead is placed in the tissue, with electrodes in contact with the nerve tissue to be stimulated. The terminal portion of the lead is tunneled subcutaneously to a site where the pulse generator means is implanted, which is usually in the abdominal area. The tissues are surgically closed in layers, and stimulation can be applied after the tissues are healed from the surgery.
In one aspect of the invention, the pulsed electrical stimulation is applied to provide therapy for, or alleviating the symptoms of prostatitus and chronic pelvic pain. For providing such therapy, the electrodes are implanted on, or adjacent to one or more of the pudendal nerve or its branches or portions thereof, or the prostatic plexus or its branches or portions thereof, or the hypogastric nerve or its branches or portions thereof. Detailed anatomy of this region is shown in conjunction with FIGS. 8A, and 8B, 8C. The placement of electrodes to provide such therapy is also shown in conjunction with FIGS. 8B and 8C, and can be at a convenient location on one or more sites of the sacral, inferior hypogastric or superior hypogastric plexus or their branches or portions thereof.
Pulsed electrical stimulation induces nerve impulses in the form of action potentials in the nerve fibers. Shown in conjunction with FIG. 9, the information in the nervous system is coded by frequency of firing rather than the size of the individual action potentials. The bottom portion of FIG. 9 shows a train of action potentials 7. Shown in conjunction with FIG. 10, the rate of action potential generation depends on the magnitude of the depolarizing current. Thus, the firing frequency of action potentials reflects the magnitude of the depolarizing current. This is one way that stimulation intensity is encoded in the nervous system, as shown in FIG. 10. Although firing frequency increases with the amount of depolarizing current, there is a limit to the rate at which neurons can generate action potentials, depending on the absolute refractory period and the relative refractory period.
In the method and system of this invention, pulsed electrical stimulation is provided using both implanted and external components. The pulse generator may be implanted in the body, or may be external to the body. In one aspect the external components may be networked over a wide area network, for remote interrogation and remote programming of stimulation parameters.